U.S. patent number 11,050,305 [Application Number 16/378,273] was granted by the patent office on 2021-06-29 for fixed-frequency voltage calibration in a wireless power transfer system.
This patent grant is currently assigned to Integrated Device Technology, Inc.. The grantee listed for this patent is Integrated Device Technology, Inc.. Invention is credited to Chan Young Jeong, Nicholaus Smith.
United States Patent |
11,050,305 |
Smith , et al. |
June 29, 2021 |
Fixed-frequency voltage calibration in a wireless power transfer
system
Abstract
Embodiments herein provide a device for calibrating a voltage
driven by a PWM signal for a circuit board. The device includes a
controller configured to generate the PWM signal according to a PWM
duty cycle value, and a voltage regulator configured to generate an
output voltage according to the PWM signal. The controller is
further configured to calibrate a relationship between the PWM duty
cycle value and the output voltage based on a plurality of
configured PWM duty cycle values and a plurality of corresponding
voltages measured from the voltage regulator, and drive the circuit
board by configuring the PWM duty cycle value based on the
calibrated relationship.
Inventors: |
Smith; Nicholaus (La Mesa,
CA), Jeong; Chan Young (San Jose, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Integrated Device Technology, Inc. |
San Jose |
CA |
US |
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Assignee: |
Integrated Device Technology,
Inc. (San Jose, CA)
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Family
ID: |
1000005648309 |
Appl.
No.: |
16/378,273 |
Filed: |
April 8, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200204011 A1 |
Jun 25, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62784289 |
Dec 21, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J
50/80 (20160201); H02J 50/10 (20160201); H04B
5/0037 (20130101); H04B 17/21 (20150115); H02J
50/90 (20160201) |
Current International
Class: |
H02J
50/10 (20160101); H04B 5/00 (20060101); H02J
7/02 (20160101); H04B 17/21 (20150101); H02J
50/90 (20160101); H02J 50/80 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; Dinh T
Attorney, Agent or Firm: Haynes and Boone, LLP
Parent Case Text
CROSS-REFERENCE
This application claims the benefit, under 35 U.S.C. .sctn. 119(e),
of co-pending and commonly-owned U.S. provisional application No.
62/784,289, filed on Dec. 21, 2018, which is hereby expressly
incorporated herein by reference.
Claims
What is claimed is:
1. A method of providing a voltage from a voltage regulator driven
by a pulse-width modulation (PWM) signal, the method comprising:
generating, in a controller, the PWM signal according to a PWM duty
cycle value that is configured to achieve a particular output
voltage from the voltage regulator according to a relationship
between the PWM duty cycle and the output voltage; generating, in
the voltage regulator, the particular output voltage according to
the PWM signal; calibrating, in the controller, the relationship
between the PWM duty cycle value and the output voltage based on
measurement by the controller of a plurality of configured PWM duty
cycle values and a plurality of corresponding output voltages from
the voltage regulator; and driving the voltage from the voltage
regulator by configuring the PWM duty cycle to achieve the voltage
based on the calibrated relationship, wherein the regulator and the
controller are mounted on a circuit board.
2. The method of claim 1, wherein generating the PWM signal
includes determining the PWM duty cycle value from the relationship
programmed, via input pins, into one or more registers of a
controller.
3. The method of claim 1, wherein calibrating the relationship
between the PWM duty cycle value and the voltage includes
performing the calibration at an initial power-up of the circuit
board, after a reset of the circuit board, or upon a calibration
command.
4. The method of claim 1, wherein the calibrating the relationship
between the PWM duty cycle value and the output voltage based on
the plurality of configured PWM duty cycle values and the plurality
of corresponding voltages measured from the voltage regulator
comprises: configuring a first PWM duty cycle value for a first PWM
signal; measuring a first output voltage from the voltage regulator
driven by the first PWM signal; configuring a second PWM duty cycle
value for a second PWM signal; measuring a second output voltage
from the voltage regulator driven by the second PWM signal; and
computing a slope for a linear relationship based on the first and
the second PWM duty cycle values, and the first and the second
output voltages.
5. The method of claim 4, wherein the computing the slope for a
linear relationship based on the first and the second PWM duty
cycle values, and the first and the second output voltages
comprises: dividing a difference between the first output voltage
and the second output voltage by a difference between the first PWM
duty cycle value and the second PWM duty cycle value.
6. The method of claim 4, further comprising: configuring a third
PWM duty cycle value as 0% for a third PWM signal; measuring the
third output voltage from the voltage regulator driven by the third
PWM signal; and determining a y-intercept of the linear
relationship as the third output voltage.
7. The method of claim 1, wherein the calibrating the relationship
between the PWM duty cycle value and the output voltage based on
the plurality of configured PWM duty cycle values and the plurality
of corresponding voltages measured from the voltage regulator
comprises: configuring a first PWM duty cycle value for a first PWM
signal; computing a first output voltage based on the first PWM
duty cycle value and the relationship; measuring an actual output
voltage from the voltage regulator driven by the first PWM signal;
comparing the first calculated output voltage with the measured
actual output voltage; and re-calibrating the relationship between
the PWM duty cycle value and the output voltage when a difference
between the first calculated output voltage and the measured actual
output voltage exceeds an acceptable error range.
8. The method of claim 1, wherein the calibrating the relationship
between the PWM duty cycle value and the output voltage based on
the plurality of configured PWM duty cycle values and the plurality
of corresponding voltages measured from the voltage regulator
comprises: computing a first PWM duty cycle value corresponding to
a target output voltage based on the relationship; configuring the
first PWM duty cycle value for a first PWM signal; measuring an
actual output voltage from the voltage regulator driven by the
first PWM signal; comparing the target output voltage with the
measured actual output voltage; and re-calibrating the relationship
between the PWM duty cycle value and the output voltage when a
difference between the target output voltage with the measured
actual output voltage e exceeds an acceptable error range.
9. The method of claim 8, further comprising: adjusting the
acceptable error range based on output voltage performance.
10. The method of claim 1, wherein the driving the circuit board by
configuring the PWM duty cycle value based on the calibrated
relationship comprises: computing a set PWM duty cycle value based
on the calibrated relationship and a target output voltage;
configuring the set PWM duty cycle value for a set PWM signal; and
generating the target output voltage according to the set PWM
signal.
11. A device for providing a voltage driven by a pulse-width
modulation (PWM) signal, the device comprising: a controller
configured to generate the PWM signal according to a PWM duty cycle
value according to a relationship between the PWM duty cycle and
voltage; a voltage regulator coupled to the control, the voltage
regulator being configured to generate an output voltage from the
PWM signal; and wherein the controller is further configured to:
calibrate the relationship between the PWM duty cycle value and the
output voltage based on measurement of a plurality of configured
PWM duty cycle values and a plurality of corresponding voltages at
the voltage regulator, and drive the voltage regulator by
configuring the PWM duty cycle value based on the calibrated
relationship to achieve the voltage, and wherein the controller and
the voltage regulator are mounted on a circuit board.
12. The device of claim 11, wherein the controller includes one or
more input pins configured to receive programmed PWM duty cycle
values associated with voltages into one or more registers of the
controller.
13. The device of claim 11, wherein the controller is further
configured to calibrate the relationship between the PWM duty cycle
value and the output voltage at an initial power-up of the circuit
board, after a reset of the circuit board, or upon a calibration
command.
14. The device of claim 11, wherein the controller is further
configured to calibrate the relationship between the PWM duty cycle
value and the output voltage based on the plurality of configured
PWM duty cycle values and the plurality of corresponding voltages
measured from the voltage regulator by: configuring a first PWM
duty cycle value for a first PWM signal; measuring a first output
voltage from the voltage regulator driven by the first PWM signal;
configuring a second PWM duty cycle value for a second PWM signal;
measuring a second output voltage from the voltage regulator driven
by the second PWM signal; and computing a slope for a linear
relationship based on the first and the second PWM duty cycle
values, and the first and the second output voltages.
15. The device of claim 14, wherein the controller is further
configured to compute the slope for a linear relationship based on
the first and the second PWM duty cycle values, and the first and
the second output voltages by: dividing a difference between the
first output voltage and the second output voltage by a difference
between the first PWM duty cycle value and the second PWM duty
cycle value.
16. The device of claim 14, wherein the controller is further
configured to: configure a third PWM duty cycle value as 0% for a
third PWM signal; measure the third output voltage from the voltage
regulator driven by the third PWM signal; and determine a
y-intercept of the linear relationship as the third output
voltage.
17. The device of claim 11, wherein the controller is further
configured to calibrate the relationship between the PWM duty cycle
value and the output voltage based on the plurality of configured
PWM duty cycle values and the plurality of corresponding voltages
measured from the voltage regulator by: configuring a first PWM
duty cycle value for a first PWM signal; computing a first output
voltage based on the first PWM duty cycle value and the
relationship; measuring an actual output voltage from the voltage
regulator driven by the first PWM signal; comparing the first
calculated output voltage with the measured actual output voltage;
and re-calibrating the relationship between the PWM duty cycle
value and the output voltage when a difference between the first
calculated output voltage and the measured actual output voltage
exceeds an acceptable error range.
18. The device of claim 11, wherein the controller is further
configured to calibrate the relationship between the PWM duty cycle
value and the output voltage based on the plurality of configured
PWM duty cycle values and the plurality of corresponding voltages
measured from the voltage regulator by: computing a first PWM duty
cycle value corresponding to a target output voltage based on the
relationship; configuring the first PWM duty cycle value for a
first PWM signal; measuring an actual output voltage from the
voltage regulator driven by the first PWM signal; comparing the
target output voltage with the measured actual output voltage; and
re-calibrating the relationship between the PWM duty cycle value
and the output voltage when a difference between the target output
voltage with the measured actual output voltage e exceeds an
acceptable error range.
19. The device of claim 18, wherein the controller is further
configured to: adjust the acceptable error range based on output
voltage performance.
20. The device of claim 11, wherein the controller is further
configured to drive the circuit board by configuring the PWM duty
cycle value based on the calibrated relationship by: computing a
set PWM duty cycle value based on the calibrated relationship and a
target output voltage; configuring the set PWM duty cycle value for
a set PWM signal; and generating the target output voltage
according to the set PWM signal.
Description
TECHNICAL FIELD
Embodiments of the present invention are related to wireless
transmission of power and, in particular, to fixed-frequency
voltage calibration in a wireless power transmitter.
DISCUSSION OF RELATED ART
Mobile devices, for example smart phones, tablets, wearables and
other devices are increasingly using wireless power charging
systems. Wireless power transfer involves a transmitter driving a
transmitter coil and a receiver with a receiver coil placed
proximate to the transmitter coil. The receiver coil receives the
wireless power generated by the transmit coil and uses that
received power to drive a load, for example to provide power to a
battery charger. The transmission coil is usually driven by a
switching circuit, which receives a regulated voltage from an input
power source. Noise, clock differences, or errors on a circuit
board can usually impair the reliability and accuracy of the
regulated voltage that is fed to the switching circuit, i.e. the
regulated voltage may deviate from a target voltage level that is
configured. The inaccuracy of the regulated voltage often has a
significant impact on the performance of the wireless power
transfer system.
Therefore, there is a need to improve the reliability of regulated
voltages in the wireless power transfer system.
SUMMARY
In view of the voltage reliability issue in the wireless power
transfer system, embodiments described herein provide a method for
calibrating a voltage driven by a pulse-width modulation (PWM)
signal for a circuit board. Specifically, the method includes
generating a PWM signal according to a PWM duty cycle value, and
then generating, via a voltage regulator, an output voltage
according to the PWM signal. The method further includes
calibrating a relationship between the PWM duty cycle value and the
output voltage based on a plurality of configured PWM duty cycle
values and a plurality of corresponding voltages measured from the
voltage regulator. The method further includes driving the circuit
board by configuring the PWM duty cycle value based on the
calibrated relationship.
Embodiments herein further provide a device for calibrating a
voltage driven by a PWM signal for a circuit board. The device
includes a controller configured to generate the PWM signal
according to a PWM duty cycle value, and a voltage regulator
configured to generate an output voltage according to the PWM
signal. The controller is further configured to calibrate a
relationship between the PWM duty cycle value and the output
voltage based on a plurality of configured PWM duty cycle values
and a plurality of corresponding voltages measured from the voltage
regulator, and drive the circuit board by configuring the PWM duty
cycle value based on the calibrated relationship.
These and other embodiments are discussed below with respect to the
following figures.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 illustrates a wireless power system 100 according to some
embodiments of the present invention.
FIG. 2 illustrates a detailed structure of the transmitting device
for voltage calibration in the wireless power transfer system,
according to embodiments described herein.
FIG. 3 illustrates a data plot diagram showing an example
relationship between V.sub.BRG and the PWM duty cycle, according to
embodiments described herein.
FIG. 4 illustrates an example logic flow diagram showing a process
of voltage calibration, according to an embodiment described
herein.
FIG. 5 is an example logic flow diagram showing process of
PWM-V.sub.BRG relationship computation and re-calibration,
according to an embodiment described herein.
DETAILED DESCRIPTION
In the following description, specific details are set forth
describing some embodiments of the present invention. It will be
apparent, however, to one skilled in the art that some embodiments
may be practiced without some or all of these specific details. The
specific embodiments disclosed herein are meant to be illustrative
but not limiting. One skilled in the art may realize other elements
that, although not specifically described here, are within the
scope and the spirit of this disclosure.
This description illustrates inventive aspects and embodiments
should not be taken as limiting--the claims define the protected
invention. Various changes may be made without departing from the
spirit and scope of this description and the claims. In some
instances, well-known structures and techniques have not been shown
or described in detail in order not to obscure the invention.
FIG. 1 illustrates a wireless power system 100 according to some
embodiments of the present invention. As illustrated in FIG. 1, a
transmitting device 102 transfers wireless power to a receive
device 104. Transmitting device 102 is powered by a direct current
(DC) input 105 (e.g., from 5V to 19V, etc.), which can be derived
from a Universal Serial Bus (USB) bus or an AC/DC power adapter.
The transmitting device 102 includes a switching circuit 110
coupled to the DC input source 105 and the transmitter coil 106.
The transistor array 110 produces an alternate current that is fed
to the transmitter coil 106, which in turn generates a time-varying
electromagnetic field. In this way, the transmitter coil 106
transfers power to the receiver coil 108 coupled to the receiving
device 104 via electromagnetic induction.
The receiver coil 108 is coupled to a rectifier circuit within the
receiving device 104, which receives and rectifies wireless power
received at the receiver coil 108, and then in turn provides an
output voltage for battery charging.
FIG. 2 illustrates a detailed structure of the transmitting device
102 for voltage calibration in the wireless power transfer system
100, according to embodiments described herein. The transmitting
device 102 includes a voltage regulator 108, which receives the
input voltage (e.g., 9V to 16V) from the power source 105 and
provides a voltage V.sub.BRG to the switching circuit 110. Voltage
regulator 108 is driven by a PWM signal 124 output from the
transmit control module 112.
The transmit control module 112 can be a dedicated transmit
integrated circuit as shown in FIG. 2. The transmit control module
112 includes a processor, which may execute processor-readable
instructions stored from a storage medium such as a memory, to
control transmitter functions, e.g., to control a PWM signal that
drives the switching circuit 110. For example, the transmit control
module 111 may configure the duty cycle (%) of a PWM signal that is
used to drive a voltage regulator 118, which in turn provides a
regulated voltage to the drain of each half-bridge in the switching
circuit 110. By generating and controlling the PWM signal, the
transmit control module 112 in turn controls the alternate current
(AC) current that passes through the transmitter coil 106. An
example of the transmit control module 112 may be the Integrated
Device Technology.RTM. P9261 chip.
The transmit control module 112 is configured to generate a second
PWM signal 124 based PWM duty cycle values (%) to drive the voltage
regulator 118 with feedback node or other method or output voltage
control. The configuration settings of the PWM cycle values may be
programmed into the registers within the transmit control module
112, via input pins 125. For example, a user or a developer may
program the PWM cycle values, or a processor of a device that
employs and controls the wireless power transfer system 100 may
program the PWM cycle values.
Due to various error or noise factors associated with a specific
circuit board on which the transmit control module 112 resides on,
the PWM signal 124 that is generated according to a specific PWM
duty cycle setting may not result in a desired regulated voltage
V.sub.BRG reliably from the voltage regulator 118. The error or
noise factors include, but not limited to external component
variation tolerances, internal clock differences, low drop-out
regulator voltage level, analog-to-digital converter (ADC) errors,
samples rates, and output noise, etc. These factors may cause
variations from circuit board to circuit board, and result in
inaccuracies in the regulated voltage V.sub.BRG even when the PWM
duty cycle settings have been programmed accordingly to achieve a
target V.sub.BRG. In addition, if any part of the transmit control
module 112 is changed or customized, the change may lead to a
completely wrong conversion from the register settings of PWM duty
cycle values to the output V.sub.BRG voltage from the voltage
regulator 118. Conventional systems only run measurement routines
of V.sub.BRG when a new V.sub.BRG voltage is set, and errors due to
board-to-board variations are usually ignored, resulting in
inaccurate and unreliable V.sub.BRG voltage applied to the
switching circuit 110 or it takes much longer to get the V.sub.BRG
to the correct value in a series of change, measure, change
approximations toward converging on the desired setpoint.
Therefore, the transmit control module 111 is configured to
calibrate the relationship between the PWM signal and the regulated
voltage that is output from the voltage regulator, based on which a
PWM duty cycle value (%) can be programmed to achieve a desired
regulated voltage for the switching circuit 110. The calibration
routine may be implemented by firmware (FW) and/or software of the
transmit control module 112. Specifically, the transmit control
module 112 is configured to execute processor-readable instructions
to calculate and configure, PWM duty cycle values to be used, when
new configuration settings (such as Digital ping voltage, Qmeas
voltage, VBRG_Max_settings, thermal throttling, etc.) are
programmed into the registers in the transmit control module 112.
The voltage regulator 118 may in turn react accordingly to the new
configuration settings by performing a sweep of the newly
configured PWM duty cycle values (e.g., 0%, 10%, 20%, . . . 80%,
90%, etc.) and monitoring the output V.sub.BRG. The relationship
between the PWM signal 124 and V.sub.BRG can thus be characterized
board-by-board (e.g., for each printed circuit board (PCB)), and
the characterized PWM-V.sub.BRG relationship may in turn be used to
calculate and set PWM duty cycle values for the PWM signal 124 to
achieve a particular V.sub.BRG. In this way, the calibration
routine may refine V.sub.BRG level on a unit-by-unit basis and
allow for aging correction.
FIG. 3 illustrates a data plot diagram showing an example
relationship between V.sub.BRG and the PWM duty cycle, according to
embodiments described herein. A linear relationship between
V.sub.BRG and the PWM duty cycle may be established, as shown at
line 312, based on previously measured V.sub.BRG and corresponding
PWM duty cycle data points such as data points 301 and 302. Board
variation manifests as differences in the slope and the intercept
of line 312. In some embodiments, a non-linear relationship between
V.sub.BRG and the PWM duty cycle may be established by applying
different regression models based on the previously measured
V.sub.BRG and corresponding PWM duty cycle data points.
FIG. 4 illustrates an example logic flow diagram showing a process
400 of V.sub.BRG calibration, according to an embodiment described
herein. At step 402, the voltage regulator 118 is operated to
generate the voltage V.sub.BRG using PWM signal 124 which is
generated by the transmit control module 112 based on PWM duty
cycle configuration. As discussed above, due to component variation
at different PCBs, the PWM duty cycle value that is configured to
achieve a particular V.sub.BRG voltage may vary board-to-board. To
calibrate the actual PWM duty cycle value used for a particular
V.sub.BRG voltage at a particular PCB, at step 404, a V.sub.BRG
calibration sweep is run to calibrate the PWM-V.sub.BRG
relationship prior to wireless power transfer at the wireless power
transfer system 100. For example, a number of example PWM duty
cycle values may be programmed to the registers in the transmit
control module 112 via the GPIO pins 125 shown in FIG. 2, and the
resulting V.sub.BRG voltage from the voltage regulator 118 is
monitored. The (V.sub.BRG, PWM duty cycle %) pair may then be
plotted to calibrate the PWM-V.sub.BRG relationship, e.g., the
linear relationship as shown by line 312 in FIG. 3, all within
reasonable limits for accuracy to force convergence to an expected
value.
Specifically, at step 408, the PWM-V.sub.BRG relationship
calibration is initiated to obtain set-point measurements at
initial power-up of the wireless power transfer system 100, after a
RESET of system 100, and/or upon receipt of a self-calibration
command.
At step 410, upon obtaining the set-point measurements, the
PWM-V.sub.BRG linear relationship may be established based on at
least two measured pairs (DUTY_A, VBRG_A) and (DUTY_B, VBRG_B) as
shown at data points 301 and 302, e.g.,
V.sub.BRG=[(VBRG_A-VBRG_B)/(Duty_A-Duty_B)].times.PWM+VBRG(0%_duty)
Thus, at step 412, in a Slope-Intercept Form, at step 412, the
slope m of the linear relationship is calculated as Rise/Run, at
which the Rise=(VBRG_A-VBRG_B), the Run=(Duty_A-Duty_B). For
example, although any two data points can be used for establishing
the linear relationship, data point (DUTY_A, VBRG_A) may be
measured at 10% duty cycle, and data point (DUTY_B, VBRG_B) may be
measured at 90% duty cycle. The y-intercepts b is obtained as the
measured V.sub.BRG at PWM of 0% duty cycle.
At step 414, the linear PWM-V.sub.BRG relationship can be obtained
as: V.sub.BRG=M.times.PWM+b, using the calculated slope and
y-intercept of the linear line 312.
FIG. 5 is an example logic flow diagram showing process 500 of
PWM-V.sub.BRG relationship computation and re-calibration,
according to an embodiment described herein. The example duty cycle
values shown in FIG. 5 and throughout the application are for
illustrative purpose only. Different duty cycle values may be used
in process 500.
At step 502, a PWM duty cycle setting of 95% is programmed to the
transmit control module 112, and the resulting V.sub.BRG_95% is
measured at the output of voltage regulator 118. At step 504, a PWM
duty cycle setting of 90% is programmed to the transmit control
module 112, and the resulting V.sub.BRG_90% is measured at the
output of voltage regulator 118, e.g., using as data point (Duty_B,
VBRG_B) 302. At step 506, further data points are obtained to
perform a spot check. For example, PWM duty cycle settings of 75%,
50%, 25% are programmed into the transmit control module 112, and
VBRG_75%, VBRG_50%, and VBRG_25% are measured, respectively. At
step 508, a PWM duty cycle setting of 10% is programmed to the
transmit control module 112, and the resulting VBRG_10% is
measured. For example, the measurement at duty cycle of 10% can be
used as data point 301 (Duty_A, VBRG_A). At step 510, the slope m
of the linear relationship is calculated using the measurements
(Duty_A, VBRG_A) and (Duty_B, VBRG_B), e.g., the measurements
obtained at PWM 10% and 90%. At step 512, a PWM duty cycle setting
of 0% is programmed to the transmit control module 112, and the
resulting VBRG_0% is measured, which represents the y-intercept
parameter b of the linear relationship.
The accuracy of the PWM-V.sub.BRG linear relationship may then be
verified, e.g., board by board, by comparing the calculated
V.sub.BRG with the measured V.sub.BRG for a particular PWM duty
cycle value. The verification may be implemented in two ways: (1)
by setting a fixed PWM duty cycle value, and measuring the
resulting V.sub.BRG versus the calculated V.sub.BRG; and/or (2) by
computing and configuring a PWM duty cycle value based on a target
V.sub.BRG, and measuring the resulting V.sub.BRG versus the target
V.sub.BRG. The verification methods (1) and (2) may be implemented
consecutively in any order, concurrently, jointly or
separately.
For example, at step 514, spot check data is calculated based on
the linear relationship, e.g., VBRG_75%, VBRG_90%, and VBRG_95% is
calculated using the linear equation V.sub.BRG=m.times.PWM+b by
setting PWM=0.75, 0.9, 0.95, respectively. The actual V.sub.BRG is
then measured by programming PWM duty cycle at 75%, 90%, 95%,
respectively. At step 516, the measured V.sub.BRG is then compared
to the calculated V.sub.BRG to determine whether a match is
verified, e.g., the difference between the measured V.sub.BRG and
the calculated V.sub.BRG, if any, is within an acceptable range,
for example to within .about.5%. When a match is verified at step
516, process 500 continues to step 520 for another round of spot
check. When the measured V.sub.BRG does not match with the
calculated V.sub.BRG, process 500 proceeds to step 502 to repeat
steps 502-514 and recalibrate the PWM-V.sub.BRG relationship.
At step 518, the PWM-V.sub.BRG relationship is further verified by:
calculating a respective PWM duty cycle value to achieve a given
V.sub.BRG value (e.g. V.sub.BRG=0.3V), based on the linear
relationship. The calculated PWM duty cycle value is then
programmed to the transmit control module 112 to generate the
corresponding PWM signal 124, under which the resulting V.sub.BRG
from voltage regulator 118 is measured. At step 520, the measured
V.sub.BRG is compared against the target V.sub.BRG value to
determine whether a match is verified, e.g., the difference between
the measured V.sub.BRG and the target V.sub.BRG is within an
acceptable range, for example to within .about.5%. If no match is
verified, process 500 goes back to step 502 to repeat steps 502-514
and recalibrate the PWM-V.sub.BRG relationship. If a match is
verified, process 500 goes to step 522. The match verification at
step 520 may be performed with multiple setpoints of (PWM,
V.sub.BRG). For example, PWM duty cycle settings can be programmed
to achieve a target V.sub.BRG of 0.3V, 4V, etc., respectively, and
the resulting V.sub.BRG are measured and compared with the targets
of 0.3V, 4V, respectively. At step 522, the setpoints (PWM,
V.sub.BRG) within the acceptable error limit can be obtained.
In some examples, the match requirements may be revised. For
example, after multiple rounds of recalibration, if none or few
matches can be verified, the acceptable error limit may be relaxed.
For another example, the acceptable error limit may be tightened
when the resulting V.sub.BRG appears to be inaccurate and thus
negatively impacts system performance. For another example,
different PCBs may yield different acceptable error limits, which
may be adjusted based on V.sub.BRG accuracy.
At step 524, process 500 transitions to the operation of wireless
power transfer system 100 using the calibrated PWM-V.sub.BRG
relationship to select and program PWM duty cycle parameters in
order to achieve a given V.sub.BRG level.
The above detailed description is provided to illustrate specific
embodiments of the present invention and is not intended to be
limiting. Numerous variations and modifications within the scope of
the present invention are possible. The present invention is set
forth in the following claims.
* * * * *